1. Field of the Invention
The present invention generally relates to surgical sutures, and more specifically relates to surgical sutures having projecting barbs used for anchoring the sutures in tissue and prosthetic devices.
2. Description of the Related Art
Surgical sutures are used for closing wounds and surgical incisions, and repairing damaged muscles, vessels, and tissue. Typically, a needle is attached to one end of the suture, and the needle is drawn through tissue to form one or more loops holding the tissue together. The suture is subsequently tied off in one or more knots so that the tissue will remain drawn together, or so that a prosthetic device will remain anchored in place.
Although sutures are very effective for closing wounds and incisions, there are a number of problems associated with conventional sutures. Many of these problems are directly related to the knots used to secure sutures in place. If the knots are not tied properly, defects may arise including slippage, knot breakage, and re-opening of the wound or incision. In addition, using knots to secure sutures may distort tissue, restrict blood flow, increase the formation of scars, impede wound healing, and result in infection.
In response to the deficiencies associated with conventional sutures, barbed sutures have been developed. Unlike conventional sutures, barbed sutures have projecting barbs that allow the suture to be used to close wounds, approximate tissue, tighten tissue, and attach prosthetic devices without using knots. U.S. Pat. No. 5,931,855 discloses a barbed suture that is used for cosmetic procedures such as brow-lifts and face-lifts.
Referring to FIG. 1, a conventional barbed suture 20 is generally formed by cutting a core thread 22 with a cutting blade 24. FIG. 1 illustrates an exemplary cut, whereby the cutting blade 24 first cuts into the core thread 22 at an angle β of approximately 30 degrees relative to a longitudinal axis x-x of the core thread to a depth of approximately 0.008 inches, and subsequently further cuts into the core thread for a distance of approximately 0.024 inches at an angle of approximately 0 degrees to form a projecting barb 26. After the cut is completed, the barb 26 remains connected to the core thread 22 through a base 28.
Performing a barb-cutting operation as shown in FIG. 1 requires the use of a mechanical shearing methodology that will rapidly dull the cutting edge of the cutting blade, thereby requiring frequent changes of the cutting blade. The cutting methodology is also negatively affected by the typical extruded diameter variation in the target thread. This variation in diameter requires a cutting head that must be frequently adjusted in fine diameter threads as small changes in thread diameter result in significantly thinner/weaker barbs, or in thicker threads resulting in thicker, stiffer barbs that will cause a variation in frictional drag during application.
The leading edge of the cuts in the core thread act as stress concentration points. In applications where a significant or pulsatile load is placed on the barbed suture, e.g., heart valve repair or replacement procedures and orthopedic applications, a given barb may fail, or begin peeling away from the core thread. Once this occurs, due to the highly oriented nature of the suture material, the barb may be stripped off the core thread along a significant length of the suture causing catastrophic failure of the suture approximation.
For example, referring to FIG. 2, after the cutting steps previously described, the cut barbs 24 remain flexibly coupled with the core thread 22 via the bases 28. When a leading end 30 of the barbed suture 20 is pulled in the direction D1, the barbs 24 collapse inwardly toward the core thread 22, and deflect toward a trailing end 32 of the barbed suture 20. When the trailing end 32 of the barbed suture is pulled in the direction D2, trailing edges 34 of the barbs 26 penetrate and engage the surrounding media. Continued motion of the suture in direction D2 causes the barbs to deflect outwardly and away from the core thread 22. As the barbed suture is pulled in the direction D2, great stress builds upon the previously cut base sections 28. As a result, one or more of the barbs 26 may fail at the base sections 28 and delaminate from the core thread 22. This type of structural failure may result in catastrophic failure of the barbed suture, which may cause serious injury to, or the death of, a patient.
In order to improve the reliability and durability of barbed sutures, some have attempted to enhance the strength of the connection between the barbs and the core thread. Unfortunately, these efforts have provided barbed sutures that are rigid or relatively inflexible when deflecting in either direction. As a result, the rigid barbs resist the necessary collapsing deflection necessary when pulled through tissue and impart significant drag and damage to the tissue during passage. The drag and tissue damage effects become exaggerated when the barbed elements are in radial opposition to each other along the core thread. When the barbs are placed in radial opposition to each other, the projected cross section of the suture with the two rigid barbs extending from the core thread result in sawing of the tissue when the suture is applied. Due to this “sawing effect”, the tissue may be damaged and the ultimate holding strength of the applied suture may be reduced.
In some instances, braided barbed sutures having more durable barbs are used. The braided barbed sutures include at least one barbed filamentary element intertwined with a plurality of unbarbed filaments to provide a barbed suture that is more rugged and durable. In one embodiment of commonly assigned U.S. Patent Application Publication No. 2007/0005110, the disclosure of which is hereby incorporated by reference herein, a prosthetic heart valve has a valve sewing ring and braided barbed sutures are disposed in the valve sewing ring by first passing the sutures through an annulus and then passing the sutures through the valve sewing ring. Approximately 12-20 sets of braided barbed sutures are passed through the valve sewing ring to secure the prosthetic heart valve in place. The heart valve is then parachuted down the sets of barbed sutures and seated in place within the annulus. After the heart valve has been parachuted down into place, the barbs prevent the valve from being moved in the opposite, upward direction for holding the heart valve in place without requiring knots. While the braided construction improves the durability of the suture, the process to produce the braided barbed suture is more extensive than the processes required for simple barbed monofilament suture.
In spite of the above advances, there remains a need for monofilament barbed sutures that may be readily manufactured and that have improved reliability, durability and efficacy. There also remains a need for barbed sutures that cause minimal or no damage to tissue as the suture is passed through the tissue while retaining their structural integrity. Moreover, there remains a need for barbed sutures that stay in place after being positioned in tissue and prosthetic devices.